Date: Sun, 6 Jun 1999 10:40:01 -0400 (EDT) From: Zhihui Zhang <zzhang@cs.binghamton.edu> To: Farshid Eslami <farshid@bol.sharif.ac.ir> Cc: freebsd-hackers@freebsd.org Subject: Re: allocate file blocks contiguously Message-ID: <Pine.GSO.3.96.990606103122.8549B-100000@sol.cs.binghamton.edu> In-Reply-To: <Pine.WNT.4.10.9906031117560.-68371-100000@ana.bol.sharif.ac.ir>
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> > For more info about maxcontig, you can refer to the well-known > paper of McKusic et al about Fast File System. It is a parameter > that is hardware dependent. You can't get performance just by > increasing its value. Unfortunately, I don't have on-line version > of that paper. > > > --Farshid > > On Wed, 2 Jun 1999, Zhihui Zhang wrote: > > > > > In FFS, there is a parameter called maxcontig (default to 16) that > > determines the number of blocks we can allocate contiguously for a single > > file. What is its optimal value? I mean, if we allocate ALL the data > > blocks of a very big file contiguously, will its I/O performance be > > improved greatly? It seems to me this number may also be limited by > > system buffering capability (MAXPHYS?) and underlying hardware controller. > > Can anyone give me some hints on the choice of the value of maxcontig? > > I read the paper at http://docs.FreeBSD.org/44doc/, which is basically the same as in the 4.4 BSD book (p276). My feeling is that if we allocate ALL the data blocks of a big file contiguously, this will lead to "too much localization" as described in the paper (or the book). However, this may be good for this big file if the system buffering capability and hardware allow it (at the cost of other files?) Regards, Zhihui To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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